Biochemical Tests

Question 0

Describe the biochemical test for reducing sugars

Answer 0

Benedicts reagent. Add to a sample and heat it but not to boiling point. If reducing sugar present it will form a coloured precipitate hich changes from blue green yellow orange brick red. Higher concentration of reducing sugar further colour change goes. Better way of comparing is to filter solution and weigh precipitate as more accurate

Question 1

Describe the biochemical test for protein

Answer 1

Biuret test. Add sodium hydroxide solution to make the test solution alkaline. Add copper (II) sulphate solution. If protein is present a purple layer forms. If not the solution will stay blue

Question 2

Describe the biochemical test for non reducing sugars

Answer 2

Eg sucrose. Boil solution with dilute hydrochloric acid and then neutralise it with sodium hydrogencarbonate. This breaks the non reducing sugars down into monosaccharides. Then carry out the test using Benedicts reagent.

Question 3

Describe the biochemical test for starch

Answer 3

Add iodine dissolved I’m potassium iodide solution to the test sample. If starch is present the sample will change from browny orange to blueblack

Question 4

Describe the biochemical test for lipids

Answer 4

Emulsion test. Shake test substance with ethanol for 1 minute then pour solution into water. If lipid is present the solution will turn milky. More lipid there is present the more noticeable the milky colour will be

Question 5

Describe how to determine glucose concentration

Answer 5

Measure the concentration of the blue Benedicts solution left after the test. Paler solution left the more glucose there was. First you must make a calibration curve then use the curve to estimate concentration based on the Absorbance value

Question 6

What does a colourimiter measure

Answer 6

Absorbance hich is the amount of light absorbe by a solution. The more concentrated th colour of the solution the higher the Absorbance

Question 7

How do you make a calibration curve

Answer 7

Make up several glucose solutions of different, known concentrations eg 10mM, 20mM, 30mM. Do Benedicts test on each solution using same amount of Benedicts reagent. Remove any precipitate in a centrifuge or by leaving for 24 hours. Use a colourimiter to measure the Absorbance of Benedicts solution remaining in each tube. Use the results to plot a calibration curve showing Absorbance against glucose concentration